Electrical Problem W/ New AC Blower Motors - High Speed Shuts Off After 15 Min? - Electrical - DIY Chatroom Home Improvement Forum


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Old 07-09-2011, 06:36 PM   #1
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


"I have 2 vertical cabinet AC units in my condo, 300 & 800 cfm, each having a 1/10 HP 115V 1050 Rpm, 3.3 amps with 5 speeds but the actual units switches only have 3 speeds.

The motors have gone bad over the past 15 yrs and I have recently bought and tried to install 3 similar motors with different but as close to the amps per HP/speed as the original motors and the same thing is happening with all 3 new motors. *The High Speed setting runs for approximately 15 minutes before it starts to smell like it is overheating and then the motor shuts down? *

The condo is 120v normal household wiring. I actually have purchased 3 diff motors. *Current one is the closest match I could find to my original motor which is: *5 inch diameter, High Speed1/10 HP @ 3.3amps, Med Speed @1.1 amps w/ 1/35th HP, Low speed @ .76 amps 1/70th HP, *115V, 1050 RPM, 5 Speed (but only use high,
med & low), Dbl Shaft 10" x 1/2", Shaded Pole, 60 HZ, Auto Overload, sleeve bearings.

2 of the motors are 1/10 HP but I could not match exact amps at high, med & low settings so the 1st one had 3.2 amps @ 1/10 HP & the other is 3.6 amps @ 1/10 HP. *3rd motor I tried was a 1/6 th HP @ 8.6 amps. *All 3 would only run for approx 15 min on high and then smelled like the motor/wires were overheating or burning and the would automatically shut down. I could wait 1/2 Hr & turn back on but after 10 min they would do the same thing & shut down? *I have been able to keep the 1/6 HP working on med for the last week without shutting down, but it does not cool my living room down enough w/90 degree + summer. *I also have been able to keep the 1/10th HP motor in my Bdr running at Med, but it shuts down on high after 10 min and smells like it's overheating?

Can you tell me is this because the new motors do not exactly match the old motor amperage at various speeds or would this be due to a bad wire from the speed switch to change speeds on the motor or a problem with my condo wires to the speed knob. I can't believe I am having the same problem with all new motors (AO Smith & Packard Ind) and in both rooms? *

Any help or pointers would be greatly appreciated. Tyndale"

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Old 07-10-2011, 01:36 AM   #2
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


If the thermal cut out in the motor is activating.
Then either the motor is faulty, or
The motor is being overloaded.
You cannot just put any motor on a set of blades,
The motor must have enough power to suit the blades,
Or the motor will over heat and shut down.
You need to double check that the motor is suitable
for the job required,
It would seem that yours might not be.

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Old 07-10-2011, 02:06 AM   #3
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


I have purchased 3 different brand new motors. All are 5 inch Dia, 115 V, 1050 RPM, 60 HZ, pole shaded, just like the prior motor (exactly the same for those specs) & the old ones were 1/10 HP starting with 3.3 amps and then the other speeds were ratcheting down from there (but my new motors have no problems running at the lower speeds). The 1st new motor was 1/10 HP @ 3.2 amps, the 2nd one was 1/10 HP @ 3.6 amps and the 3rd was a 1/6 HP @ 8.6 amps. All motors stopped working on high speed after approx 10-20 minutes and smelled like they were overheating. After they sutomaticcally shut down I was able to turn them back on in a half Hr and I put them on med and low and they work fine. So, Grainger and Packard told me they were almost the same and would work (I took my old motors with spec plates so they could match) and they said all 3 should work.

I then can assume that on high they are being overloaded and that is why the Home Depot electrician thought the capacitor in the thermostat has gone bad on the high setting, because med and low settings the motors work fine? Would that br correct?
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Old 07-10-2011, 02:27 AM   #4
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


It is worth checking the caps,
Cant say for sure if it is the problem,
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Old 07-10-2011, 02:31 AM   #5
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


Are there any blockages in the vents,
that could be placing undue loads on the fan motors ?
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Old 07-10-2011, 02:43 AM   #6
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


No, I have cleaned all of the vents and there are no blockages. ? While I'm somewhat electrically challenged, I assume to check the caps I would take the cover off of the thermostats and the use my multiple meter to check the current / Amps while I turn the speed to High? To check the load from the thermostat to the motor? If it reads more then 3.3 amps, then the motors are most likely being overloaded on high? And if so, then I need a new thermostat?
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Old 07-10-2011, 04:58 AM   #7
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Electrical Problem w/ New AC Blower Motors - High Speed shuts off after 15 Min?


That is not the best way to check the caps,
To properly check them you need to check two things,
The capacitance, some digital type meters will have this function.
Also and probably most importantly you need to check the esr,
This is "equivilent series resistance" this requires a special type meter,
But many television repair shops will have one,
Perhaps take it to your local repairer and ask if they will test it.
Some visual checks can also locate problems,
look for leaks, buldges and obvious overheating.
If not sure just replace them.
Most a/c and refrigeration suppliers will have them.
The most important check is the esr test,
it will surely locate any problems.

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